Wind tunnel model and method

ABSTRACT

A wind tunnel model having pressure measurement orifices formed integrally therein and a process for making same.

United States Patent [1 1 *[111 3,791,207 [451- Feb. .12, 1974 Jackson,Jr. et al.

[ WIND TUNNEL MODEL AND METHOD [75] Inventors: Charlie M. Jackson, Jr.,Yorktown;

Dallas G. Summerfield, Hampton, both of Va.

[73} Assignee: The United States of America as represented by theNational Aeronautics and Space Administration, Washington, DC.

[22] Filed: June 19, 1972 [21] App]. No.: 263,815

52 US. a. 73/147 [51] Int. Cl. G0lm 9/00 [58] Field of Search 73/147[56] References Cited UNITED STATES PATENTS 2,523,481 9/1950 Rabenhorst73/147 2,551,526 5/1951 Campbell 2,602,329 7/1952 Clark 73/147 PrimaryExaminerS. Clement Swisher Attorney, Agent, or FirmHoward J. Osborn;Wallace J. Nelson; John R. Manning [5 7] ABSTRACT A wind tunnel modelhaving pressure measurement orifices formed integrally therein and aprocess for making same.

- 8 Claims, 4 Drawing Figures WIND TUNNEL MODEL AND METHOD ORIGIN OF THEINVENTION This invention was made by employees of the NationalAeronautics and Space Administration and may be manufactured-or used byor for the Government of the United States without the payment of anyroyalties thereon or therefor.

BACKGROUND OF THE INVENTION The aerodynamic characteristics of wings andother airfoil surfaces are normally evaluated by wind tunnel tests onsmall scale models. Much of the experimental aerodynamic research datais obtained by measuring the surface pressures on models of specificconfigurations in the wind tunnel. The construction of the models andinstallation of the necessary pressure orifices has heretofore been adifficult and expensive task. For example, prior art methods forconstruction of pressure-test models of airfoils have included castingor ma chining the desired test shape for the airfoil with the pressureorifices then installed by one of two techniques depending on theairfoil thickness and the nature of the data tobe obtained. If the testairfoil is sufficiently thick, slots are machined in the airfoil surfaceand steel tubing embedded in the slots with clear plastics. The orificesare then drilled through the plastic and into the tubing. For thinairfoils, the tubing is installed through the airfoil from the oppositeside of the pressure orifices desired and attached to the wing in anexposed position on that side.

When the technique of embedding the tubes in the surface is used, it isdifficult to maintain the airfoil shape. The process of installing thetubing through the airfoils is also undesirable because the aerodynamick shape of the surface opposite to the instrumental side is destroyed bythe presence of the tubing and if the airfoil is not symmetrical themodel must be reinstrumented or remade to provide the surface pressureson the opposite side.

It is therefore an object of the present invention to provide new andnovel wind tunnel models.

Another object of the present invention is a novel method of makingaerodynamic wind tunnel models having integrally formedpressureinstrumentation capabilities. I A further object of the presentinvention .is a simplified method of making aerodynamic wind tunnelmodels having pressure orifices therein.

An additional object of the present invention is a novel method ofproviding orifices to a wind tunnel test model. I

The foregoing and other objects are attainable in the present inventionby clamping a plurality of diverse length, small diameter tubularmembers in fixed spaced relationship, casting an aerodynamic modelconfiguration about one end of the assembled tubular members,

ing the clamping fixture and the even length portions of the tubularmembers exposed for subsequent connection with suitable conventionalpressure measurement instrumentation.

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein:

FIG. 1 is a view of an assembled array of tubular members clampedtogether prior to casting of the aerodynamic configuration therearound;

FIG. 2 is a side view of the clamped tubular array shown in FIG. 1;

FIG. 3 is a view of an aerodynamic airfoil wind tunnel model constructedin according with the present invention; and

FIG. 4 is a side view of a modified airfoil wind tunnel model accordingto the present invention.

' Referring now to the drawings, FIGS. 1 and 2 show a tubular array asemployed in the present invention and generally designated by referencenumeral 10. Tubular array 10 includes a plurality of small diametertubular members 12 clamped in spaced parallel adjacency by a pair ofclamp blocks 14 and 16. A pair of countersunk screws 18 and 20 serve tosecure blocks 14 and 16 together. Suitable channels are machined orotherwise formed in the opposed faces of clamp blocks 14 and 16 so as toreceive tubular member 12 therebetween in tight fixed relationship. Asshown in the drawings, tubular members 12 are of diverse lengths with anequal length of each tube extending from one side of blocks 14 and 16andwith the uneven lengths thereof extending from the other side of blocks14 and 16. The even length tubes are those disposed at the base of theconstructed airfoil while the uneven lengths are designed to extend tovarying distances within the airfoil toward the leading edge thereof.

Referring now to FIGS. 3 and 4, two finished airfoil body configurationsare shown as constructed in accordance with the present invention and asgenerally designated, respectively, by reference numerals 30 and 40.These airfoil models utilize the tubular array of FIGS. 1 and 2 and areformed by casting a metal or other solidifiable material 31 and 41around the tubular array 10 so as to completely encase the uneven lengthportions of tubular members 12. The'even length portions of tubularmembers 12 and clamp blocks 14 and 16 are left exposed. Aftersolidification of the casting material 31-, the clamp blocks 14 and 16are removed and sufficient lengths of the tubular members 12 are leftexposed for connection with suitable and conventional pressuremeasurement instrumentation. After casting the material 31, for example,about an array of tubular members 12, the airfoil is finished andpolished in a conventional manner to achieve the precise desiredexterior configuration.

An X-ray photo is then taken of the airfoil body 30 to precisely locatethe individual tubes 12 therein. Tubes 12 are crimped or otherwiseclosed at the embedded ends thereof prior to the casting operation toprevent any solid casting material from entry therein. The x-ray film isthen used as a template to permit drilling of transverse holes 33, onefor each tubular member 12, to intersect perpendicularly with theindividual tubular members 12. Holes 33 are positioned at the points onairfoil model 30 where pressure measurements are desired during a windtunnel test and tubular members 12 are connected to conventionalpressure measurementinstrumentation during testing.

FIG. 4 is similar to FIG. 3 but of a different configuration and showingpressure openings drilled in only one surface of body 41 of airfoil 40.It is to be understood that such openings may be made in any surface ofthe airfoil so as to intersect with the tubular members 12.

Although no specific material has been mentioned for the airfoil bodies,it is to be understood that any material normally used for modelairfoils is considered within the scope of the present invention. In aspecific example 355 aluminum alloy was used for the cast airfoil bodyand stainless steel S.A.E. 30347 -0.065 inch O.D. was used for thetubing to cast an airfoil of 16 inch chord and 4 inch semi-span. In thisexample, seventy pressure orifices 33 of 0.040 inch diameter weredrilled through the airfoil body portion 31 to intersect with a likenumber of tubular members 12.

As mentioned hereinbefore, the tubing core is constructed by clampingthe desired number of tubes 12 in the proper configuration with a splitblock of aluminum or the like. The uneven lengths of the tubing are thencrimped or otherwise sealed to prevent molten cast material from entrytherein. The tubing block, formed of clamp blocks 14 and 16 is closed intight engagement with the tubing via countersunk screws 18 and 20 andserves in conjunction with the pattern 40 to form the part of the moldcommonly referred to as the core print. An aluminum model is then castin the normal way with the tubing core in position in the casting mold.The aluminum alloy referred to hereinbefore is heated to a pourtemperature of l,350 F. Where steel tubing is used for members 12 thenormal casting shrinkage and differences in the thermal expansionbetween aluminum and steel insure a sufficiently tight bond between thetubing and model such that no leaks occur. The casting is then finishedto the desired shape in a conventional manner and the x-rays taken toprovide templates for drilling the pressure orifices as describedhereinbefore.

Alternate embodiments of the model casting process described hereinwould include different tubing core configurations, shapes other thanfor airfoil bodies and alternate methods of securing the tubing core inthe mold other than the clamp blocks shown. For example, the tubingarray could be formed by welding each of the tubular members to anadjacent member. Also, various improvements over conventional coatingtechniques, such as preheating the tubing core 10 to essentially thetemperature of the molten casting metal to minimize thermal warpage isalso considered within the scope of the present invention.

Thus, it is readily seen that the present invention provides a novelprocess of making wind tunnel airfoil models for pressure measurementsthereof that results in an improved model that exhibits more reliabilitythan previous models and a process that reduces the cost of providinginstrumented pressure models to essentially one-half of the cost ofprior art methods.

There are obviously many modifications and variations of the presentinvention possible in the light of the above teachings. It is thereforeto be understood that within the scope of the appended claims theinvention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A method of making a perforated metal structure having preciselocations of the perforations therein comprising the steps of: p

a. assembling a plurality of tubular members in fixed,

spaced relationship,

b. casting a material around said plurality of tubular members so as tocompletely enclose one end of the assembled tubes,

f. finishing the cast structure to the desired specifications whilemaintaining one end of the tubular members open,

(1. x-raying the finished structure to establish the precise location ofthe individual tubes,

e. drilling a hole through the cast structure to intersect with eachindividual tube at the desired distance along the length thereof and byusing the x-ray film as a template.

2. The method of claim 1 'wherein said perforated I metal structure isan airfoil designed for wind tunnel testing and the cast metal isselected from the group consisting of aluminum and aluminum alloys.

3. The method of claim 2 wherein said tubular members are formed of thinwalled steel and wherein the ends of the steel tubes embedded in thecast structure are crimped closed prior to casting of the metal.

4. The method of claim 1 wherein the plurality of tubular members are ofdiverse lengths and are clamped together in spaced relationship prior tocasting the metal structure therearound.

5. A method of constructing an aerodynamic wind tunnel test model havinga series of openings therein for making pressure measurements at diverselocations on the model during a wind tunnel test, comprising the stepsof:

a. providing a plurality of tubular bodies of diverse lengths in a fixedarray,

b. closing one end of each of said tubular bodies,

c. casting a solid material about said tubular bodies so as to form anaerodynamic configuration there about that embeds the closed ends of thetubular bodies adjacent the leading edge of the configuration whileleaving the open ends thereof exposed at the trailing edge of theconfiguration,

d. drilling a hole perpendicular to the individual tubular bodiesthrough the cast solid so as to form an intersecting passagewayperpendicular with the passageway in each of the tubular bodies and eachperpendicular passageway being a different distance from the leading andtrailing edge of the aerodynamic configuration than an adjacentpassageway whereby pressure sensing instrumentation may be connected tothe open end of each tubular body adjacent the trailing edge of theaerodynamic configuration to thereby make pressure measurements on thewind tunnel model at diverse locations thereof during a wind tunneltest.

6. The method of claim 5 wherein said tubular bodies are clamped betweentwo aluminum blocks to form the fixed array.

7. The method of claim 5 wherein the cast solid mate- 'rial is selectedfrom aluminum and aluminum alloys cation along the length of theindividual tubular bodies.

1. A method of making a perforated metal structure having preciselocations of the perforations therein comprising the steps of: a.assembling a plurality of tubular members in fixed, spaced relationship,b. casting a material around said plurality of tubular members so as tocompletely enclose one end of the assembled tubes, f. finishing the caststructure to the desired specifications while maintaining one end of thetubular members open, d. x-raying the finished structure to establishthe precise location of the individual tubes, e. drilling a hole throughthe cast structure to intersect with each individual tube at the desireddistance along the length thereof and by using the x-ray film as atemplate.
 2. The method of claim 1 wherein said perforated metalstructure is an airfoil designed for wind tunnel testing and the castmetal is selected from the group consisting of aluminum and aluminumalloys.
 3. The method of claim 2 wherein said tubular members are formedof thin walled steel and wherein the ends of the steel tubes embedded inthe cast structure are crimped closEd prior to casting of the metal. 4.The method of claim 1 wherein the plurality of tubular members are ofdiverse lengths and are clamped together in spaced relationship prior tocasting the metal structure therearound.
 5. A method of constructing anaerodynamic wind tunnel test model having a series of openings thereinfor making pressure measurements at diverse locations on the modelduring a wind tunnel test, comprising the steps of: a. providing aplurality of tubular bodies of diverse lengths in a fixed array, b.closing one end of each of said tubular bodies, c. casting a solidmaterial about said tubular bodies so as to form an aerodynamicconfiguration thereabout that embeds the closed ends of the tubularbodies adjacent the leading edge of the configuration while leaving theopen ends thereof exposed at the trailing edge of the configuration, d.drilling a hole perpendicular to the individual tubular bodies throughthe cast solid so as to form an intersecting passageway perpendicularwith the passageway in each of the tubular bodies and each perpendicularpassageway being a different distance from the leading and trailing edgeof the aerodynamic configuration than an adjacent passageway wherebypressure sensing instrumentation may be connected to the open end ofeach tubular body adjacent the trailing edge of the aerodynamicconfiguration to thereby make pressure measurements on the wind tunnelmodel at diverse locations thereof during a wind tunnel test.
 6. Themethod of claim 5 wherein said tubular bodies are clamped between twoaluminum blocks to form the fixed array.
 7. The method of claim 5wherein the cast solid material is selected from aluminum and aluminumalloys and said tubular bodies are formed of stainless steel.
 8. Themethod of claim 5 wherein an x-ray print is made of the cast solidmaterial and said x-ray print is employed as a template to preciselylocate the individual tubular bodies to permit drilling of theperpendicular hole through the cast solid material at a precise locationalong the length of the individual tubular bodies.